Humans have mostly been reliant to the light that the sun provides. In the time before electricity, work starts once the sun rises, and ends once it sets. Since time has become an important factor in our lives, we shift it as required. In the US, daylight saving time maximizes the sun's availability by shifting the time. It also isn't useless since it brings a lot of benefits. Adjusting the work schedule seems to lower accidents since there is more light on the road. People are able to sleep more comfortably. There are savings in electricity, etc.